Thanks for the suggestions.
Called the manufacturer. They told me that they need to pull a radiator off the shelf in the warehouse to find out the thrad width on the draincock (do they know what they’re manufacturing??)! I guess I have to buy a new draincock from a different manufacturer that fits; this manufacturer doesn’t sell directly anyway and as far as I know there are no spare CSF draincocks sold through distributors. Aftermarket has its disadvantages.
Do you have a CSF 2568 a.k.a CSF W0133-1605833 radiator by any chance in your Honda?
Thanks!